The device for detecting the states of the vehicle's driver such as the drowsy driving state and the inattentive driving state is needed to detect a pupil of the driver from a taken image of the driver. However, in case that the driver wears glasses, the pupil may be hidden behind a frame of the glasses. In this case, the device can not correctly detect the pupil of the driver, thereby resulting in the fact that the device is needed to obtain information indicating whether the pupil is hidden or not. One of the methods to obtain the information is known as including steps of detecting the frame of the glasses, and detecting whether the pupil is hidden behind the detected frame (see, for example, Patent Document 1).